Preparation of metallo porpyrins and photoinducued electron transfer from porphyrins to biointerface

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Photoinduced electron transfer systems, which changes light energy to high-energy electrons, are model systems of natural photosynthesis to harvest solar energy. Electron acceptor linked photosensitizers are one of good system to generate long lifetime charge separated species by light illumination. The charge separated species, however, are achieved in not water solution but organic solvent. There is intense interest in experiments which reveal how achieve charge separated species in aqueous solution. We report that long lifetime charge separated specie in water is generated and that photoinduced hydrogen evolution occurs effectively.Hydrophobic porphyrin-butylviologen-aminopropylviologen triad molecules undergo a photoinduced two-step electron transfer reaction which results in the generation of reduced viologen with a lifetime on the microsecond time scale in aqueous solution. Structure of the viologen linked porphyrin is shown in Fig. 1. The viologen linked porphyrin has a gradually hydrophilic molecule from hydrophobic porphyrin to aminopropylviologen, and facilitates a directional electron transfer to the aminopropylviologen in water, because the two viologen moieties stay under a linear arrangement which shows no intramolecular interaction with face to face of pi-electron between viologens and between the porphyrin ring and viologen. The gradually hydrophilic form also facilitates solvent cages for electron transfer from the phoexcited porphyrin to adjacent viologen, so that electron transfer via the photoexcited singlet state occurs in aqueous solution. The porphyrin was also applied for photoinduced hydrogen evolution system, and effective hydrogen evolution was observed.